Transverse CT image in a 34-year-old man with acute right lower quadrant pain caused by appendicitis with perforation. Appendiceal lumen (short black arrow) is enlarged and shows wall enhancement. Mesenteric stranding (white arrow), free intraperitoneal air (arrowhead), and thickened terminal ileum (long black arrow) due to contiguous inflammation are seen.

radiology.rsna.org/content/240/3/623.full